Magnetic properties of singlet ground states in RM2X2 compounds

A simple survey of the magnetic properties of new tetragonal RM2X2 compounds is given. Particular attention is paid to the interaction of Crystal Field in the case of nonmagnetic singlet ground states. A number of physical effects which result from this situation are discussed. In particular, the nature of this type of ground state is proved to be indispensable for the existence of amplitude magnetic structures at 0 K and for the most amazing of mixed magnetic phases, in which Rare Earth ions with two magnetic states are involved. Evidence of this behaviour through several examples in such compounds as PrNi2Si2, TbNi2Si2, TbRu2Si2 and TbRu2Ge2 from the joint analysis of different magnetic properties will be presented. (C) 1998 Elsevier Science S.A.